1. Field of the Invention
The invention relates to a process for producing welded pipes from copper and copper alloys in a combined production line, comprising a casting installation for raw materials, a hot-rolling mill, a pipe-shaping and welding section and a drawing device for the welded pipe.
2. Discussion of the Prior Art
In the field of copper pipes and pipes made from copper alloys, a distinction is drawn between seamless pipes and welded pipes.
Seamless pipes are produced, for example, by the following process routes: continuous solid casting, extrusion, cold pilger rolling and drawing, although the cold pilger rolling may optionally be omitted. It is also known for the solid strand to be pierced in a cross-rolling piercing process, followed by cold pilger rolling and then drawing to its final dimensions. Processes in which a hollow strand is cast, which is then subjected to the drawing operation after the cold pilger rolling, should also be mentioned. All the processes described involve drawbacks; extrusion entails high production costs, and continuous hollow casting does not provide adequate quality of pipe. Moreover, pipes which are produced in seamless form have poor wall-thickness tolerances.
Welded pipes are generally produced from continuous-cast slabs which are roughed in hot-rolling mills for sheet metal, followed by cold-rolling, slitting and welding. Following the welding operation, the pipes are drawn using standard drawing processes. A drawback of the pipe-welding processes are the high costs of producing strip, which make the pipes uneconomical to produce.
The strip is produced using various processes. The process usually encompasses the continuous casting of slabs, hot-rolling of the slabs, milling of the surfaces, followed by cold-rolling, coiling of the cold-rolled strip and subsequent slitting into narrow strips which are fed to further processing stations. The advantage of the cold strip produced in this way resides in the high capacities of more than 100,000 t/a (metric tons per year) which can be achieved in combination with a good surface quality. The discontinuity of the process and the high production costs constitute drawbacks.
An alternative process involves the casting of thin slabs, which obviates the need for hot-rolling of broad strip. Then, in this case too, the surfaces of the strip are milled, before the strip is cold-rolled, coiled and slitted into narrow strips. This process can be carried out continuously, and mean capacities of less than 100,000 t/a can be achieved in combination with a good surface quality. This process also has the drawback of excessively high production costs.
A third process is known as the high reduction process. In this case, the strip is cast into graphite molds at a casting speed v=1 m/min, the surfaces are milled, the strip is cold-rolled with a high reduction per pass, is coiled and is slit into narrow strips. This process can be operated continuously, and the surface qualities which can be achieved are good. The low capacities of around, 10,000 t/a, together with the high production costs, constitute drawbacks of this process.
The object of the present invention is to provide an improved process for producing inexpensive pipes with a high dimensional accuracy and surface quality from copper and copper alloys, in which process rolled strip is processed into longitudinally welded pipes. The aim is that the process should be suitable for economically producing relatively small quantities up to relatively large quantities (between 10,000 and 100,000 t/a).